#include<bits/stdc++.h>
using namespace std;
int n;
int f(int s){
	if(s==1) return 0;
	if(s==2) return 1;
	else return (s-1)*(f(s-1)+f(s-2));
}
int main(){
	cin>>n;
	cout<<f(n); 
    return 0;
}
/**************************************************************
	Problem: 1694
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/